#include<bits/stdc++.h>
using namespace std;
int main()
{
	char a[25];
	cin.getline(a,20);
	int len=strlen(a),js=0;
	
	for (int i=0; i<len; i++)
	{
		if (!(a[0]>='0'&&a[0]<='9')) 
		{
			if ((a[i]>='0'&&a[i]<='9')||(a[i]>='a'&&a[i]<='z')||(a[i]>='A'&&a[i]<='Z')||(a[i]=='_')) js++;
		}
		else 
		{
			cout<<"no"<<endl;
			return 0;
		}
	}
	if (js==len) cout<<"yes"<<endl;
	else cout<<"no"<<endl;
	
	return 0;
}